Our studies during the year will continue to focus on histidine biosynthesis and mechanisms of chemotaxis in Salmonella. In addition, we plan on using Salmonella and E. coli as instruments to delineate those metabolic pathways responsible for metabolic activation of otherwise inert compounds to carcinogens/mutagens. Finally, experiments on the interaction of Pseudomonas and Proteus strains will be continued. Bibliographic references: Hartman, P.E., Hulbert, P.B., Bueding, E., and Taylor, D.D. 1975 Microsomal activation to mutagens of antischistosomal methyl thioxanthenones and initial tests on a possibly non-mutagenic analogue. Mutation Res. 31:87-95; Ino, I., Hartman, P.E., Hartman, Z., and Yourno, J. 1975 Deletions fusing the adjacent hisG and hisD genes of the Salmonella histidine operon. Abstr. Ann. Mtg. Amer. Soc. Microbiol., #H89, p.111.